In human and non-human primates, trophoblasts invade the uterus and uterine vasculature. Endovascular trophoblasts migrate against the flow of blood, reaching uterine spiral arteries which they remodel. Trophoblast-endothelial interaction is essential for establishing a blood supply to the fetus. Impaired trophoblast invasion and incomplete vascular remodeling occur in preeclampsia and intrauterine growth restriction. Identification of regulatory mechanisms controlling trophoblast invasion will provide a better understanding of placental development and insights into the etiology of these disorders. Endovascular trophoblasts are exposed to blood flow-derived shear stress (FSS) but little is known about how FSS regulates trophoblast-endothelial interaction and trophoblast function. During the previous funding period, we showed for the first time that 1 integrin expression and trophoblast migration were stimulated by physiological levels of FSS. Trophoblast 1 integrin is upregulated during invasion and is important in adhesion and migration on endothelium. 1 Integrin is downregulated in preeclampsia. This application addresses the question: how does FSS induce trophoblast 1 integrin expression and trophoblast migration on endothelium? Based on new data, we have developed a hypothesis that invokes new roles for the cell-surface mucin, MUC1. These data show that (1) FSS-mediated upregulation of 1 integrin is attenuated in trophoblasts in which MUC1 expression is silenced (2) FSS induces phosphorylation of trophoblast MUC1 and co-localization of MUC1 and epidermal growth factor receptor (ErbB1) (3) FSS-mediated upregulation of 1 integrin involves estrogen receptors (ERs), and (4) FSS causes accumulation of ER in nuclei and this is not seen when MUC1 expression is silenced. We propose that MUC1 forms part of a flow sensing network in endovascular trophoblasts that regulates integrin expression and trophoblast migration. In this hypothesis, FSS induces ErbB-mediated phosphorylation of the MUC1 cytoplasmic domain and phosphorylated MUC1 interacts directly with ERs. MUC1 then regulates ER function (and ultimately 1 integrin expression) by altering the nucleocytoplasmic localization of ERs. We will continue to use early gestation rhesus monkey trophoblasts as well as a novel rhesus trophoblast stem cell line and uterine microvascular endothelial cells as models to test these ideas. Aim 1 determines whether FSS-induced upregulation of trophoblast 1 integrin expression and migration on endothelium depend on ErbB-mediated phosphorylation of MUC1. Aim 2 tests whether FSS- mediated upregulation of trophoblast 1 integrin expression and migration require interaction between MUC1 and ERs. Aim 3 determines whether FSS-induced upregulation of trophoblast 1 integrin expression and migratory activity depend on MUC1-mediated phosphorylation of ERs. Aim 4 determines whether MUC1 modulates ER function by regulating the intracellular localization of ERs. The final aim uses an optical trap to determine whether cell surface MUC1 responds to directly applied force.